Many electric machines, such as electric motors and electric generators, include a stator and a rotor that rotates around a rotor rotation axis adjacent the stator. Such electric machines may use magnetic flux to transfer power between the stator and the rotor. The rotor of some electric machines includes permanent magnets that create north magnetic poles of the rotor and permanent magnets that create south magnetic poles of the rotor. Magnetic flux may flow from the permanent magnets forming the north magnetic poles of the rotor, through the stator, to the permanent magnets forming the south magnetic poles of the rotor. In the case of axial-flux electric machines, the magnetic flux may flow across an axial gap in the direction of the rotor rotation axis as it flows between the rotor and the stator.
Unfortunately, axial-flux electric machines often have all of their permanent magnets mounted to an outer surface of the rotor, such as with adhesive. This may provide a relatively weak connection between the permanent magnets and the rotor, which may preclude operating the electric machine in manners and/or circumstances that would cause high forces on the permanent magnets. For example, attaching permanent magnets to an outer surface of the rotor of an axial-flux electric machine may preclude rotating the rotor at high speeds because high centrifugal forces may detach the permanent magnets from the rotor.
Published U.S. Patent Application No. 2005/0029886 A1 to Van Tichelen et al. (“the '886 application”) shows an axial-flux electric machine having permanent magnets that are clamped into a rotor. The axial-flux electric machine shown by the '886 application includes a rotor and a stator disposed adjacent one another along an axis that the rotor rotates about. Each of the permanent magnets of the '886 application is disposed in a passage extending through the rotor parallel to the axis that the rotor rotates about. Plates bolted to the side of the rotor adjacent the stator cover the ends of the passages adjacent the stator, and a ring of material bolted to an opposite side of the rotor covers the ends of the passages opposite the stator. In the axial-flux electric machine disclosed by the '886 application, each permanent magnet creates a magnetic pole of the rotor.
Although the '886 application shows an axial-flux electric machine with permanent magnets clamped into its rotor, certain disadvantages persist. For example, using a single permanent magnet to create each magnetic pole of the rotor of an axial-flux electric machine may limit the power potential of the axial-flux electric machine because a single permanent magnet may produce a relatively weak magnetic field. Additionally, using a single permanent magnet to create each magnetic pole of the rotor of an axial-flux electric machine may limit the constant power speed range of the axial-flux electric machine when the axial-flux electric machine operates as an electric motor.
The axial-flux electric machine and methods of the present disclosure solve one or more of the problems set forth above.